1. Field of the Invention
The present invention relates to projection exposure apparatuses and to projection exposure methods. More specifically, the present invention relates to a projection exposure apparatus and to a projection exposure method in which both a line width in an isolated pattern and a line width in repeated patterns are accurately controlled.
2. Description of the Related Art
In a lithography process, lines formed on a substrate have become increasingly fine. Accordingly, the lines are required to have uniform width with high accuracy. In a uniform pattern, line widths are easily controlled by adjusting the exposure level.
However, in a case in which a mask includes both a pattern of repeated lines and a pattern of an isolated line, it is difficult to control the line widths of both patterns to be within a tolerance range at the same time.
FIG. 9 is a schematic representation of an example of a mask pattern including repeated lines (dense part) and an isolated line (isolated part). The line width in the dense part and the line width in the isolated part are the same in the mask. As a result of a projection exposure, however, the widths of the lines formed on a substrate of, for example, a semiconductor wafer, are different from each other. Even when the projection exposure is performed while the substrate surface (resist surface) is disposed at the best focus position of a projection optical system in an exposure apparatus, the line width in the dense part, Ld, and the line width in the isolated part, Li, differ after developing the resist on the substrate. Accordingly, it is necessary to control a CD (critical dimension) bias “B”, which is defined in the descriptions herein as B=(Ld−Li).
Even when a plurality of projection lenses, which are manufactured with the same design, are used, the CD bias “B” differs in accordance with the wavefront aberration, which differs between individual lenses. In addition, it has been discovered that the CD bias “B” varies with the half-width of a laser beam for exposure which affects the chromatic aberration, and with the wavefront aberration, which varies with the temperature of the projection lens which depends on an exposure history.
In addition, it has also been discovered that the variation of the CD bias “B” also occurs due to vibration of a stage.
In addition, the CD bias “B” also differs in accordance with line widths, kinds of patterns, kinds of masks (binary mask, halftone mask, etc.), and illumination conditions (annular illumination, quadrupole illumination, normal (circular) illumination).